The proposed research addresses potential molecular processes involved in lesion-induced changes in precise neuronal circuitry during development. Our aim is to determine the role of Eph proteins in the mouse auditory brainstem during deafferentation-induced plasticity. Our experiments focus on the ventral cochlear nucleus (VCN), which normally projects to the contralateral, but not ipsilateral, medial nucleus of the trapezoid body (MNTB). The VCN-MNTB projection is part of the circuitry used for the computation of interaural intensity differences and is essential for sound localization. Following unilateral deafferentation during development, the intact VCN forms an additional aberrant projection to the ipsilateral MNTB. The molecular signals that regulate the development of the VCN-MNTB pathway and this form of plasticity are incompletely understood. Experiments performed in our laboratory provide evidence to support the hypothesis that Eph receptor tyrosine kinases and their ligands, the ephrins, are involved in these processes. This proposal focuses on ephrin-B2 and one of its receptors, EphB2, because preliminary studies suggest that reverse signaling elicited by EphB2 through ephrin-B2 is necessary for the restriction of the VCN-MNTB projection to the contralateral side. We will evaluate the roles of ephrin-B2 and EphB2 in deafferentation-induced plasticity during early and late development following cochlear nucleus removal. Using neuroanatomical tracing techniques, post-deafferentation projection patterns of mice with mutations in ephrin-B2 or EphB2/EphB3 will be compared to those of wild type littermates. Ephrin-B2 and EphB2 expression in VCN and MNTB will also be examined during development and following unilateral deafferentation with the use of immunohistochemistry and in situ hybridization histochemistry. PUBLIC HEALTH RELEVANCE: Findings from the proposed project will yield valuable information regarding recovery following brain injury, especially to the auditory system. More specifically, it may provide beneficial insights into therapies for congenital hearing disorders by uncovering mechanisms of neural reorganization and plasticity during development. Furthermore, findings may provide results that could aid in the development of therapeutic strategies to assist recovery from injury to the central auditory system during adulthood.